There’s an old French wisecrack that goes something like this: A man of a certain age at a soirée waves away a flute of bubbly and when asked why responds, “I never drink Champagne — it makes me think of the war.” A similarly acid dynamic appears to be at work as France now grapples with an explosive mix of social turmoil and inflation. 

With President Macron’s popularity sinking to new lows, his economy and finance minister, Bruno Le Maire, has penned a novel containing explicit sex scenes that have made him the laughing stock of Paris. 

In an ironic twist, the novel, called “Fugue Américaine” or “American Runaway,” was published on the same day last week that the Fitch credit ratings agency downgraded France’s debt worthiness one notch to AA-. In dinging the rating, Fitch cited factors including weak fiscal metrics, high government debt, and “social unrest that complicates policy-making.” It raises the question: Where is your economy minister when you need him?

Writing in his spare time is the more charitable answer, but French newspaper Libération had another: “Runaway Minister,” one headline thundered. Others evoked fresh headaches for Mr. Macron’s embattled administration. Thanks to the power of the internet, one particularly racy passage from the book quickly made the rounds of social media; it mocked not just the prose but its purveyor, the 54-year-old Mr. Le Maire, who has been Mr. Macron’s right-hand finance man since 2017. 

There is no doubt that Monsieur Le Maire is a talented writer. Like Mr. Macron, he is a graduate of the now defunct École nationale d’administration, the most prestigious of France’s grande écoles and effectively a finishing school for the most ambitious French political leaders. He is also the winner of a major French literary prize. 

Yet the fine prose and unusual plot notwithstanding — two brothers travel to Havana to attend a performance by Vladimir Horowitz — his latest work appears to lean more toward “Last Tango in Paris” than Stendhal. 

While the French are not known to be bashful about depictions of sex in literature and art, this book hits a little differently. The French historian Oliver Vartan mocked the minister’s audacious oeuvre on Twitter, writing that “the government has started a help hotline for people who stumble upon Bruno Le Maire’s erotic texts inadvertently.”

Lawmaker François Ruffin of the left-wing France Unbowed party, which is led by Jean-Luc Mélenchon (who ran against Mr. Macron in presidential elections twice), was less wry, writing: “at a time when the French people have huge worries about inflation … should [Mr. Le Maire] have one minute, one hour, one week of his time to dedicate to writing erotic scenes?”

Another member of that party, Thomas Portes, tweeted: “Inflation is exploding, millions of people can’t eat or fill their fridge, pay their rent. France is fighting the pension reform. And during this time, the minister Bruno Le Maire writes novels. Right to the end, they’re throwing contempt in our face.”

Monsieur Le Maire has in fact written five novels since taking up the mantle of managing the French economy. Amid the present furor, he took to social media to defend himself, writing, “Many of you are asking me how I find the time to write when I’m a minister. Some people do gardening or go hiking, I write.” 

Moonlighting as a novelist is, according to the 54-year-old father of four, a way of finding “personal balance.”

Now safely into his second term, there is little risk of immediate political fallout for Mr. Macron. Yet the unapologetic tone-deafness of his economic minister will do nothing to bolster his plummeting popularity. According to the latest survey, 70 percent of the French consider Mr. Macron to be a “bad president.” 

That same survey indicates that a majority of French are in favor of dissolving the National Assembly — the legislative body that Mr. Macron essentially bypassed to push through his unpopular pension reform, which has set off weeks of protests and police clashes in France. 

At the same time, the approval rating of Mr. Macron’s chief rival on the right, Marine Le Pen, has risen to a record 34 percent. Her National Rally party won 89 seats in the most recent parliamentary elections. Mr. Macron will have a hard time squaring off against Ms. Le Pen over important legislative matters, and he knows it. 

All of Mr. Macron’s political rivals, who are growing in number, will see the disconnect between the economy minister and the now downgraded French economy as a sign of growing chaos in the country that is becoming harder to contain. 

Things were so bad on the streets recently that King Charles had to cancel a visit to Paris, pivoting to Germany instead. 

The relative quiet from the National Rally over the past tumultuous months in France is deceptive. Ms. Le Pen is not the only French politician waiting to capitalize on Mr. Macron’s growing catalog of blunders, but she is arguably the best prepared, as well as best organized.

On May Day, Ms. Le Pen was not at Paris discussing books but visiting the port city of Le Havre, in order to be, as she put it, “among her people.” That meant the working class, the members of which are the ones struggling to keep up with the rising cost of cheese and crackers while Mr. Macron’s economy chief writes about imagined sexual antics in 1940s Cuba.